1. Technical Field
The present invention relates in general to polarization rotation in horizontal cavity, surface emitting lasers and, in particular, to an improved system, method and apparatus for the use of horizontal cavity, surface emitting lasers for thermally assisted recording in hard disk drives.
2. Description of the Related Art
Horizontal cavity, surface-emitting lasers, or HCSELs, have been developed in recent years to combine some of the best properties of conventional, end-firing diode lasers and vertical-cavity surface-emitting lasers (VCSELs). Such lasers have an output that is generally polarized in the plane of the underlying wafer. Some applications, however, require polarization rotation to properly orient the laser polarization relative to the target.
For example, some implementations of thermally assisted recording (TAR) heads for hard disk drives require rotation of the polarized laser light beam. This step is useful since the normal polarization coming from the laser is orthogonal to the polarization at the near field aperture used in TAR. Rotating the polarization within the slider waveguide is accomplished by structures that are very difficult to fabricate and greatly complicate an already difficult fabrication process. Furthermore the efficiency of polarization rotation for the very short device lengths required in the slider remains to be demonstrated.
FIGS. 2A-2C depict a mirror-integrated laser diode 21, commonly referred to as a HCSEL. Laser diode 21 produces a beam 23 that is directed through the laser cavity and reflected downward by a facet 25 as a reflected beam 27 toward a target. Importantly, the reflected beam 27 is polarized (see reference arrow 33) in a direction that is orthogonal to a longitudinal direction of the laser diode 21.
For some applications, however, the polarization of the reflected laser beam must be reoriented in a direction that aligns with the track direction. Examples of prior art techniques for reorienting a polarized beam include discrete components such as half-wave plates, non-linear effects in fibers or active elements using Faraday or Kerr effects. Discrete components are not feasible for small scale applications due to their large size and cost. Moreover, some techniques are wavelength dependent. Mode-locked lasers often use nonlinearity-induced polarization rotation, which requires high power and is also prohibitive in terms of size and cost. Polarized continuous wave crystalline lasers (see, e.g., U.S. Pat. No. 3,914,710) induce thermal stress in the laser rod via optical pumping to cause polarization rotation. Although these conventional solutions are workable in certain applications or with specific devices, an improved design that works for HCSELs would be desirable.